1. Field of the Invention
This invention relates generally to turbomachinery and, more particularly, to an improved assembly for retaining blades in a turbomachinery rotor.
2. Description of the Prior Art
In the manufacture of bladed turbomachinery rotors, effective retention of the aerodynamic blades on a rotor disk has been a continually recurring problem. The most common method currently being used to secure the blades to their supporting rotor disk is that of employing blade dovetail tangs which are disposed within individual axial dovetail slots around the periphery of the rotor disk. This method has proven to be very effective for the purpose of withstanding the radial loads of the centrifugal force of the rotor. However, since there are also considerable axial forces on the blades, particularly with respect to blade tip rubs, foreign object impacts and secondary impacts resulting from foreign object damage, it is also necessary to provide for positive axial blade retention in both axial directions.
Many different and varied devices and mechanisms have been utilized in the past to axially retain the rotor blade dovetails within the dovetail slots. While many of these prior art devices and mechanisms are relatively effective, they are usually complex in nature and expensive to produce. They also add unnecessary weight to the rotor which tends to decrease overall operating efficiency.
When the rotor blades are large, as for example in the case of a high bypass fan for a gas turbine engine, interlocking blade shrouds are commonly employed to prevent excessive blade deflection and to dampen vibration. To facilitate the removal and/or replacement of an individual shrouded blade from a fully assembled rotor it is common to radially oversize the dovetail slot so that a blade may be moved radially inwardly a sufficient distance in order to clear the adjacent blade shrouds. When such radially oversized dovetail slots are utilized it is necessary to hold each blade radially tight against its individual dovetail slot since experience has shown that even a relatively small amount of tangential freedom of the blade tang within its dovetail slot permits relative motion during periods of windmilling. Such relative motion may cause excessive wear of the dovetail slot protective coating which in turn may permit increased galling wear of the dovetail slot as well as the mating blade shroud faces, thereby resulting in increased maintenance expenses and reduced disk life. While some prior art blade retainers have been successful in preventing such relative motion, they are also usually expensive to produce and add unnecessary weight to the rotor.